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Document the internal alpha channel format better, and fixes for 32bit alpha bitmaps.

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For images, rows need to be even (this is not true for anti-aliased font files).
Fix stride and size calculation. This makes images that have odd pixel rows display properly and fixes buffer overflows.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@30966 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Thomas Martitz 2011-11-11 19:05:11 +00:00
parent 158e14a8c6
commit 312b2a2de7
3 changed files with 33 additions and 13 deletions
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30
firmware/drivers/lcd-16bit-common.c
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@ -229,6 +229,25 @@ void lcd_mono_bitmap(const unsigned char *src, int x, int y, int width, int heig
lcd_mono_bitmap_part(src, 0, 0, width, x, y, width, height);
}
/* About Rockbox' internal alpha channel format (for ALPHA_COLOR_FONT_DEPTH == 2)
*
* For each pixel, 4bit of alpha information is stored in a byte-stream,
* so two pixels are packed into one byte.
* The lower nibble is the first pixel, the upper one the second. The stride is
* horizontal. E.g row0: pixel0: byte0[0:3], pixel1: byte0[4:7], pixel2: byte1[0:3],...
* The format is independant of the internal display orientation, as to
* support the same font files on
* The values go linear from 0 (fully transparent) to 15 (fully opaque).
*
* This might suggest that rows need to have an even number of pixels.
* However this is generally not the case. lcd_alpha_bitmap_part_mix() can deal
* with uneven colums (i.e. two rows can share one byte). And font files do
* exploit this.
* However, this is difficult to do for image files, especially bottom-up bitmaps,
* so lcd_bmp() do expect even rows.
*/
#define ALPHA_COLOR_FONT_DEPTH 2
#define ALPHA_COLOR_LOOKUP_SHIFT (1 << ALPHA_COLOR_FONT_DEPTH)
#define ALPHA_COLOR_LOOKUP_SIZE ((1 << ALPHA_COLOR_LOOKUP_SHIFT) - 1)
@ -357,17 +376,16 @@ static void ICODE_ATTR lcd_alpha_bitmap_part_mix(const fb_data* image,
dmask = 0xffffffff;
drmode &= DRMODE_SOLID; /* mask out inversevid */
}
if (drmode == DRMODE_BG)
{
dmask = ~dmask;
}
/* sourcing from an image ignore drawmode.
* Set to DRMODE_BG as we use its code path in the switch below */
if (image != NULL)
{
dmask = 0;
drmode = DRMODE_BG;
}
if (drmode == DRMODE_BG)
{
dmask = ~dmask;
}
dst_row = LCDADDR(x, y);
@ -560,7 +578,7 @@ void ICODE_ATTR lcd_bmp_part(const struct bitmap* bm, int src_x, int src_y,
else if (bm->alpha_offset > 0)
lcd_alpha_bitmap_part_mix((fb_data*)bm->data, bm->data+bm->alpha_offset,
src_x, src_y, x, y, width, height,
bitmap_stride, bm->width);
bitmap_stride, ALIGN_UP(bm->width, 2));
else
lcd_bitmap_transparent_part((fb_data*)bm->data,
src_x, src_y, bitmap_stride, x, y, width, height);